Experimental demonstration of Fresnel zone plate lens for robust subwavelength focusing at mega hertz

Xiao Pan; Longsheng Zeng; Yong Li; Xuefeng Zhu; Yabin Jin

doi:10.1016/j.ultras.2022.106876

Experimental demonstration of Fresnel zone plate lens for robust subwavelength focusing at mega hertz

Ultrasonics. 2023 Feb:128:106876. doi: 10.1016/j.ultras.2022.106876. Epub 2022 Oct 17.

Authors

Xiao Pan¹, Longsheng Zeng², Yong Li³, Xuefeng Zhu⁴, Yabin Jin⁵

Affiliations

¹ School of Aerospace Engineering and Applied Mechanics, Tongji University, 200092 Shanghai, China.
² School of Physics and Innovation Institute, Huazhong University of Science and Technology, 430074 Wuhan, China.
³ Institute of Acoustics, School of Physics Science and Engineering, Tongji University, 200092 Shanghai, China. Electronic address: yongli@tongji.edu.cn.
⁴ School of Physics and Innovation Institute, Huazhong University of Science and Technology, 430074 Wuhan, China. Electronic address: xfzhu@hust.edu.cn.
⁵ School of Aerospace Engineering and Applied Mechanics, Tongji University, 200092 Shanghai, China. Electronic address: 083623jinyabin@tongji.edu.cn.

PMID: 36272298
DOI: 10.1016/j.ultras.2022.106876

Abstract

Acoustic focusing with high energy intensity, broadband and few side lobes properties are highly demanded in many fields and can be achieved with Fresnel zone plate (FZP) lens as an artificial structure. However, FZP focusing lenses for high frequency range such as around 5 MHz with precise focusing effect has not been demonstrated and the dependence of the size, especially the full width at half maximum (FWHM), of the focal spot has not been well explored. In this work, we numerically and experimentally study the FZP lenses for robust and subwavelength underwater sound focusing effect around 5 MHz. Stable subwavelength FWHM of the focusing spot over a broad frequency range is achieved. It is found that the FWHM has a quasi-linear relationship with the ratio between the focal length and the diameter of the lens. A quasi-linear relationship between the focal length and working frequency is also validated theoretically, numerically and experimentally. Our study proposes broadband and robust FZP lenses paving the way for high quality acoustic focusing at Mega Hertz frequency range for the development of imaging, non-destructive evaluation, and so on.

Keywords: Fresnel zone plate; Metasurfaces; Subwavelength focusing.